Carbon Nanotubes (CNT) are good candidates to replace copper for use as interconnect lines (trenches) and vias in future semiconductor devices. It is shown that for relevant interconnect lengths the resistance of the optimal CNT interconnect is about an order of magnitude smaller than the resistance of a copper interconnect. When fully ballistic transport can be achieved in the carbon nanotubes, the improvement in resistance is larger, up to several orders of magnitude.
To achieve the electrical requirements set out by the International Technology Roadmap for Semiconductors (ITRS), for Back End Of Line (BEOL) interconnect trenches (lines) and vias, high quality straight horizontal and vertical metallic single-walled carbon nanotubes (SW-CNT) of very small diameter are required in extremely high density bundles (when arranged in a hexagonal packing configuration, the highest theoretically feasible CNT density is 2 CNT/nm2 assuming a tube diameter of 0.4 nm and an interspacing of 0.34 nm). The synthesis of ultra-small diameter carbon nanotubes (CNTs) necessary for achieving these very high densities of isolated SW-CNT, is up till now reported in confined circumstances e.g. by Wang et al. (Nature, 408, 50-51, 2000), by Qin et al. (Nature, 408, 50, 2000), by Hayashi et al. (Nano Letters, 3, 887-889, 2003), by Balkus Jr. et al. (Studies in Surface Science and Catalysis, 154, 903-910, 2004), and by Corma et al. (Microelectronic Engineering (2008), doi: 10.1016/j.mee.2008.01.061). The confinement effect of a mono dimensional pore seems to be crucial to synthesize the desired diameter nanotube.
Carbon nanostructures have been made in prior art by the template technique, using porous Alumina Oxide (AAO) as reported by Kyotani et al. (Chemistry of Materials, 8, 2109-2113, 1996), using mesoporous materials such as MCM-41 as reported by Urban et al. (Chemical Physics Letters, 359, 95-100, 2002) or using an AFI type zeolite as reported by Tang et al. (Applied Physics Letters, 73, 2287-2289, 1998).
Since zeolites have high pore densities in agreement with the strict requirements for CNT, they are very good candidates to produce highly dense aligned and isolated CNT within these pores. However to really exploit the interesting properties of zeolites for carbon nanostructure growth in patterned structures such as trenches and vias, zeolite growth must be integrated in the CMOS technology platform.
Furthermore, high yields of carbon nanostructure growth must be achieved. In prior art the highest pore filling degree reported is 28% by addition of hydrocarbon gas during pyrolysis. The addition of complexes to the zeolite synthesis solution or gel has been reported. However to allow zeolite crystallization, the concentration of these complexes in the zeolite synthesis gel or solution should be low, resulting in inefficient growth of carbon nanostructures (Studies in Surface Science and Catalysis, Vol. 154, pp. 903).